Willard van Orman Quine

First published Fri Apr 9, 2010; substantive revision Mon Dec 1, 2014

Willard Van Orman Quine (1908–2000) worked in theoretical philosophy
and in logic. (In practical philosophy—ethics and political
philosophy—his contributions are negligible.) He is perhaps best
known for his arguments against Logical Empiricism (in particular, its
use of the analytic-synthetic distinction). This argument, however,
should be seen as part of a comprehensive world-view which makes no
sharp distinction between philosophy and empirical science, and thus
requires a wholesale reorientation of the subject.

In what follows, a very brief section on Quine’s life and work
is followed by an overview, which will serve to orient the reader. The
third section is devoted to Quine’s arguments against the use
that the Logical Empiricists made of the analytic-synthetic
distinction, and the view that he worked out to take its place. The
subsequent three sections go systematically through Quine’s own
views; the final section is on Quine’s place in the history of
philosophy.

Quine’s philosophical thought is remarkably consistent over
the course of his long working life. There are, of course,
developments, as he comes to appreciate difficulties in his view, or
its implications, or distinctions that need to be made. Outright
changes of mind, however, are relatively rare and mostly on relatively
minor points. We can, for the most part, treat him as having a single
philosophical orientation, to which what he calls naturalism is
fundamental. This is not to say that his naturalism is self-conscious
and explicit from the start; it is, rather, something that he became
clearer about over the years.

The term “naturalism” has been understood in various
ways; we need to see what Quine’s naturalism comes to. At one
point, he describes naturalism as “the recognition that it is
within science itself, and not in some prior philosophy, that reality
is to be identified and described” (1981, 21). Two points
are important to note about the idea of “science” here.
First, it is less restrictive than it may seem. Quine certainly takes
the natural sciences, especially physics, as paradigmatic. As he says
himself, however, he uses the word “science” broadly; he
explicitly includes psychology, economics, sociology, and history (see
1995, 49). Second, Quine does not see scientific knowledge as different
in kind from our ordinary knowledge; he sees it, rather, as the result
of attempts to improve our ordinary knowledge of the world:
“Science is not a substitute for common sense but an extension of
it” (1957, 229). The scientist, he says, “is
indistinguishable from the common man in his sense of evidence, except
that the scientist is more careful” (1957, 233). We might add
that the scientist is more narrowly focused on issues of truth and
objectivity and, as contributing to these goals, clearer and more
systematic.

Many philosophers would no doubt accept that the methods and
techniques of science are the best way to find out about the world.
(With or without the points just noted about the word
“science”.) The distinctiveness of Quine’s naturalism
begins to emerge if we ask what justifies this naturalistic claim: what
reason do we have to believe that the methods and techniques of science
are the best way to find out about the world? Quine would insist that
this claim too must be based on natural science. (If this is
circular, he simply accepts the circularity.) This is the revolutionary
step: naturalism self-applied. There is no foundation for
Quine’s naturalism: it not based on anything else.

The point here is that Quine denies that there is a
distinctively philosophical standpoint, which might, for example,
allow philosophical reflection to prescribe standards to science as a
whole. He holds that all of our attempts at knowledge are subject to
those standards of evidence and justification which are most explicitly
displayed, and most successfully implemented, in the natural sciences.
This applies to philosophy as well as to other branches of knowledge.
The epistemologist, therefore, reflects on science from within science;
there is no theory of knowledge distinct from science.
(“Epistemology”, Quine says, “…is contained in
natural science, as a chapter of psychology”; 1969, 83.)

In Quine’s view, philosophers can, therefore, do no better
than to adopt the standpoint of the best available knowledge, i.e.
science, in some suitably broad sense. We adopt what he calls
“the fundamental conceptual scheme of science and common
sense” (1960, 276). Philosophers are thus to be constrained by
scientific standards. In (1974) he puts it this way: “In our
account of how science might be acquired we do not try to justify
science by some prior and firmer philosophy, but neither are we to
maintain less than scientific standards. Evidence must regularly be
sought in external objects, out where observers can jointly observe
it…” (174, 34f).

The view sketched above has both positive and negative aspects. The
latter is better-known and Quine is perhaps often thought of as a
negative philosopher, primarily concerned to criticize others. He casts
doubt on terms which many philosophers take for granted. He does not
dismiss such terms as meaningless, but simply as not meriting
a place in serious science, or in the objective account of the world at
which science aims. A well-known and important example is his criticism
of the idea of meaning. Quine says: “Meaning… is a worthy
object of philosophical and scientific clarification and analysis,
and… it is ill-suited for use as an instrument of philosophical
and scientific clarification and analysis” (1981, 185). The term
is insufficiently clear, and putative explanations which employ it are
in fact unexplanatory. (By engendering the illusion of explanation they
tend to impede the progress of science; this may well account for
Quine’s animus against the term.) It follows, in Quine’s
view, that philosophers should not rely on the term.

Quine makes similar remarks about “thought”,
“belief”, “experience”, “necessity”
and other terms which many philosophers assume are legitimate and
available for philosophical use without themselves requiring
explanation and justification in other terms. He says about the
first two on this list (and would no doubt extend the comment to the
others): “If some one accepts these notions outright for such
use, I am at a loss to imagine what he can have deemed more in need of
clarification and analysis than the things he has thus accepted”
(1981, 184).

This criticism of the scientific and philosophical use of certain
ordinary terms goes along with rejection of philosophical questions
which make essential use of those terms. The term
“knowledge” is an example. He finds the word vague, and
consequently rejects it for serious use, saying that the word is
‘‘useful and unobjectionable in the vernacular where we
acquiesce in vagueness, but unsuited to technical use because of
lacking a precise boundary’’ (Quine, 1984, 295). Many
philosophers have found the vagueness or unclarity of the term to be a
fertile field in which to cultivate what they take to be important
philosophical problems: What exactly are the conditions on knowledge?
Do we really know anything at all? For Quine, by contrast,
such questions may simply be dismissed.

As we have just seen, Quine’s views issue in very general
criticism of much philosophy. (Far more than is generally recognized.)
It is, nevertheless, a mistake to think of him as primarily a critical
or negative thinker. His criticisms rely on his positive doctrine;
articulating and defending that doctrine generates its own questions
and problems. As for whether those are genuinely philosophical
questions and problems, it is implicit in what has already been said
that he would not acknowledge such a category as the ‘genuinely
philosophical’ if that is meant to imply questions which
are different in kind from those of science. But certainly he accepts
that some questions are sufficiently general, abstract, and remote from
experiment and observation, that they may be classified as
philosophical. At times he assimilates the questions with which he is
concerned to those which have traditionally occupied philosophers. An
example is scepticism, and epistemology more generally, although
Quine’s approach to these subjects is quite different from that
of many philosophers.

In some places, Quine approaches epistemology through the problem of
scepticism about the external world. Quine has no room for the kind of
scepticism which asks the following kind of question: even if our
alleged knowledge, our science, is completely successful in its
predictions, how do we know that it tells us the way the world really
is? Thus he says: “What evaporates is the transcendental question
of the reality of the external world…” (1981, 22). The
next paragraph enlarges on the theme:

Our scientific theory can go wrong, and precisely in
the familiar way: through failure of predicted observation. But what
if… we have achieved a theory that is conformable to every
possible observation, past and future? In what sense could the world
then be said to deviate from what the theory claims? Clearly in
none…. (1981, 22; emphasis added).

There is, however, a way of understanding the sceptical question which
Quine can make sense of. Invoking gestalt psychology, he argues that
the simple sensory idea which Berkeley and Hume had claimed were given
by the senses are not in fact given, that we see things in
three-dimensions, for example, instead of having to infer the
third. He does not, however, claim that there is no problem
here. Rather, he says, “the problem was real but wrongly
viewed” (1974, 2). “The crucial logical point”, he
continues, “is that the epistemologist is confronting a
challenge to natural science that arises from within natural
science” (loc. cit.). What is the challenge? It starts
with the what Quine takes to be “a finding of natural science
itself… that our information about the world comes only through
impacts on our sensory receptors” (1990a, 19). The sceptical
challenge is then: “How … could one hope to find out about
that external world from such meager traces? In short, if our science
were true, how could we know it?” (1974, 2).

Scepticism, understood in this fashion, is a challenge to
Quine’s form of naturalism. It claims that our knowledge cannot
be accounted for in terms which are, by Quine’s standards, purely
naturalistic. Quine’s response is thus to sketch an austerely
naturalistic account of how our knowledge, and the cognitive language
in which that knowledge is embodied, arises, or might arise. This
project, as he sees it, is both essential to the defence of his
naturalistic world-view and “an enlightened persistence”
(1974, 3) in the problem that had motivated earlier epistemologists;
section 4. will go into a little more detail about the project.

When Quine asks: “How… could one hope to find out about
that external world from such meager traces?” this is not a
rhetorical question. It is, rather, a serious question, to be answered
by deploying the full resources of our knowledge—it is a
scientific question. Quine recognizes that the question, thus
construed, is not exactly what earlier epistemologists had in mind, but
argues that the change is justified: “A far cry, this, from the
old epistemology. Yet it is no gratuitous change of subject matter, but
an enlightened persistence rather in the original epistemological
problem” (1974, 3).

The defence and articulation of Quine’s naturalism thus
requires Quinean epistemology, an analogue, at least, of traditional
epistemology but carried out as a scientific enterprise. It also
requires that he set out just what is to be included in a naturalistic
account of the world; in other words, it requires an account of the
world, a least in broad outline. Among other things, this account
constrains his epistemology, since it is a naturalistic account of
knowledge that is required.

In what follows, we shall sometimes speak of Quine’s account
of the world as his “metaphysics”, but it is metaphysics
naturalized: it is not carried out a priori, or by reflection
on the nature of Being quâ Being, or anything of that
sort. (Quine himself does not much use the word
“metaphysics” but he does speak freely about ontology, and
advances substantive ontological views.)

Quine’s approach to his naturalistic analogue of metaphysics
is through the idea of regimented theory. Regimented theory is
our overall science, the sum total of our best and most objective
knowledge about the world, reformulated in the clearest and simplest
form. Quine sees this kind of reformulating as of a piece with ordinary
scientific endeavour, but carried further than working scientists are
likely to have reason to do. He discusses the distorting effect which
language is likely to have on our view of the world and comments:

To some degree…the scientist can enhance
objectivity and diminish the interference of language, by his very
choice of language. And we [meaning we philosophers, we scientists at
the abstract and philosophical end of the spectrum], concerned to
distill the essence of scientific discourse, can profitably purify the
language of science beyond what might reasonably be urged upon the
practicing scientist. (1957, 235)

Regimented theory is, of course, an idealization. It is not a
complete and finished object, available for us to examine.
Quine’s reflections on it might be considered as something like a
thought-experiment: if we were to set about assembling our total theory
of the world and recasting it in the best form, what would it look
like? Since the enterprise is not in fact going to be carried out all
the way we are not going to get a complete answer. But on some
important general issues, Quine holds, we can get answers. In
particular, he argues that the framework of regimented theory is
first-order logic with identity, that the variables of this theory
range over physical objects and sets, and that the predicates of the
theory, the only non-logical vocabulary, are physicalistic, in his
somewhat complicated sense. (See section 4, below.) Although this is
not traditional a priori metaphysics, we should not
underestimate the ambition of the project. He says of his regimented
theory that “all traits of reality worthy of the name can be set
down in an idiom of this austere form if in any idiom” (1960,
228) and speaks of “limning the true and ultimate structure of
reality” (1960, 221). The claim that the variables of
regimented range only over physical objects and sets is, as far as he
is concerned, the same claim as that only physical objects and sets
really exist.

The philosophers who most influenced Quine were the Logical
Empiricists (also known as Logical Positivists), especially Rudolf
Carnap. The distinction between analytic truths and synthetic truths
plays a crucial role in their philosophy. Analytic truths might be
characterized as those true solely in virtue of the meanings of the
words they contain; synthetic truths, by contrast, state matters of
extra-linguistic fact, and are known by experience. The Logical
Empiricists accounted for truths which do not seem to be answerable to
experience, most obviously the truths of logic and mathematics, by
saying that they are analytic, and this position was very widely held
by the 1940s. Quine, however, famously casts doubt on
analytic-synthetic distinction, and rejects the use made of it by
the Logical Empiricists and other philosophers from the 1930s on.
(Notable among the others is C. I. Lewis, first a teacher and then a
colleague of Quine; his influence on Quine has perhaps been
underestimated. See Baldwin 2013.)

The issues here are complex, and the argument takes many twists and
turns. The aim of this section is to give an account of Quine’s
mature view, and of the strongest arguments that he has for it.

Carnap holds that the role of philosophy is to analyze and clarify
the language of science, and to formulate and recommend alternative
languages. He holds that there are languages which differ in expressive
power, not merely as notational variants. (The difference between
intuitionistic logic and classical logic is an important example here,
as is the difference between the language of Newtonian mechanics and
the language of relativistic mechanics.) He also holds that there is no
one correct language. Different languages may be useful for
different purposes; it is no part of the philosopher’s job to
prescribe this or that language, merely to analyze, to clarify, and to
suggest alternatives. This idea has become known as the Principle of
Tolerance; from the 1930s on, it is fundamental to Carnap’s view
of what philosophy is and how it differs from science. (That there is
such a difference is a point which Carnap never questions.)

The Principle of Tolerance requires that, for any language, there be
a clear difference between the analytic sentences of the language and
its synthetic sentences. The former are (roughly) those which are
constitutive of the language: if we change our mind about the truth of
such a sentence we have, in effect, adopted a new language. Carnap
speaks of a change of this sort as external, since it involves a change
of language. A change of mind about an ordinary synthetic sentence is,
by contrast, internal, since it takes place within a given language.
External changes are a matter for tolerance, whereas internal changes
are correct or incorrect, not matters to which we should apply the
Principle of Tolerance. For the principle to make sense, each sentence
of the language must fall clearly into the one category or the
other.

At least as Quine sees the matter, the use of the Principle of
Tolerance also requires that analytic sentences be on an entirely
different epistemological footing from synthetic sentences. Synthetic
sentences are answerable to evidence; analytic sentences are a matter
of the choice of language, which does not require theoretical
justification.

Quine rejected the idea that there is epistemological a difference
of this kind. Even if we can distinguish the analytic sentences from
the synthetic sentences, we may still have reasons to reject an
analytic sentence. And those reasons may be of the same kind that lead
us to reject synthetic sentences. This point is hard to see if one
focuses on examples such as “All bachelors are unmarried”.
The matter is otherwise if one considers examples such as “Force
equals mass times acceleration”. (See Putnam, 1962.) A change of
mind about an analytic sentence would be a change in the language.
Still, we might have reasons to make such a change, reasons that are of
the same sort that lead us to make revisions to synthetic
sentences.

This is the view that Quine argues for. On the one hand, he
emphasizes the point (which Carnap largely accepts) that choice of
language is not theoretically neutral: some choices will make for a
better theory than others. On the other hand, he argues that the sort
of ‘pragmatic’ factors which Carnap had accepted as playing
a role in choice of language, such as simplicity, also play a
role in the choice of a theory within a language. Hence, he claims, the
two sorts of choice are on the same epistemological footing, and the
Principle of Tolerance is unjustified.

Quine’s argument for this position relies on holism.
This is the claim that most of our sentences do not have implications
for experience when they are taken one-by-one, each in isolation from
the others. What has experiential implication is, in most cases, not an
individual sentence but a larger chunk of theory. Holism is not a very
controversial doctrine. Carnap accepts it (see Carnap, 1934, 318), but
Quine holds that he does not think through its implications far enough.
In particular, Quine claims that holism shows that most of our
sentences are not justified by the relation of the individual sentence,
considered in isolation, to experience. Almost always, what matters is
the relation to experience of some larger chunk of theory (and, in
principle, although perhaps never in practice, of the theory as a
whole). This means that the correctness of a given claim is almost
never settled simply by gathering empirical evidence. Other factors
will play a role, in particular the way in which accepting that claim
would contribute to the efficacy and simplicity of the theory as a
whole. But these are precisely the ‘pragmatic factors’
which Carnap thought played a role in the choice of language. In
arguing that such factors play a role throughout our knowledge, Quine
accepts ‘a more thorough pragmatism’ (1951, 46) which
puts Carnap’s external changes on the same epistemological status
as his internal changes.

If logic, mathematics, and other putatively a priori parts
of our knowledge, are not to be explained by analyticity, how are they
to be accounted for? Holism, which is central to Quine’s argument
against Carnap, also provides him with an alternative position. Logic
and mathematics seem to have a special status because they are
independent of experience. They appear to be necessary and not
susceptible of refutation by what future experience brings; they appear
to be a priori because we know them independent of experience.
Carnap sought to explain these appearances by appealing to the idea
that accepting an analytic sentence goes with speaking the language,
and to the Principle of Tolerance. Since choice of language is not
justified by experience, the truth of the analytic sentences of a given
language is not answerable to experience.

How is Quine to explain the apparent necessity and a priori
status of some truths without appeal to the Principle of Tolerance? To
take the second point first: Quine’s holism is the view that
almost none of our knowledge is directly answerable to
experience. (The exceptions are what he calls ‘observation
sentences’; see 4.2, below.) In almost all cases the relation is
indirect: a given sentence is only answerable to experience if a
significant body of theory is presupposed. (When we say that a given
observation confirms or refutes a given theoretical claim, we are
tacitly presupposing much theoretical knowledge.) This is most easily
seen if we consider a highly theoretical sentence, of theoretical
physics, perhaps, but in Quine’s view it holds, of almost all our
sentences. The reason to accept a sentence is its contribution to the
success of theory as a whole as an efficient and simple method of
dealing with and predicting experience; in principle, this means the
success of our theory as a whole, the whole body of sentences that we
accept, in dealing with experience as a whole.

This statement, in Quine’s view, holds with full generality.
In particular, it applies to the sentences of logic and mathematics as
much as any other subject. No particular experience confirms ‘2 +
2 = 4’; Quine is not advancing what Frege derided as a
‘gingerbread and pebble’ account of arithmetic (Frege
1884, vii), in which the sentence is justified by our
observations of cookies or stones. But Quine does hold that the
sentence, and the theory of arithmetic of which it is an inseparable
part, earns its place in our body of knowledge by contributing to the
overall success of that body of knowledge in dealing with experience as
a whole.

As for the apparent necessity of some sentences, Quine appeals to
holism to explain that too. Some sentences have great systematic import
for our knowledge as a whole. (In Quine’s well-known metaphor,
they stand near the centre of the ‘web of belief’.) The
truths of elementary arithmetic are an example: they play a role in
almost every branch of systematic knowledge. For this reason, we cannot
imagine abandoning elementary arithmetic. Doing so would mean
abandoning our whole system of knowledge, and replacing it with an
alternative which we have not even begun to envisage. Nothing in
principle rules out the possibility that the course of experience will
be such that our present system of knowledge becomes wholly useless,
and that in constructing a new one we find that arithmetic is of no
use. But this is a purely abstract possibility, certainly not something
we can imagine in any detail. So the idea that we might reject
arithmetic is likewise unimaginable.

As we have just seen, even sentences which we cannot imagine
rejecting might, in principle, be rejected. As Quine says: ‘no
statement is immune to revision’ (1951, 43). This claim of
Quine’s has attracted a good deal of attention, and is sometimes
thought to be shocking or even paradoxical. In the context of his
debate with Carnap, however, it is not, by itself, at all surprising.
For Carnap too, any sentence can be revised; he would insist, however,
that in the case of some sentences, the analytic ones, a revision
involves a change of language, and thus of the meaning of the words
used in the sentence. So the idea of meaning, and sameness of meaning,
occupies a crucial role in the debate over analyticity.

In Quine’s initial arguments against the analytic-synthetic
distinction, he seeks to cast doubt on the idea that there is a notion
of meaning which is clear enough to use in defining a notion of
analyticity. (See especially Quine 1951.) Here too a crucial role
is played by holism. One apparently clear conception of meaning is that
the meaning of a sentence is given by the experiences which would
confirm it; holism, however, implies that the idea of confirmation does
not apply to individual sentences, considered in isolation from the
theories of which they are parts.

Quine’s scepticism about the idea of meaning is much
criticized. We will mention two criticisms. First, what standards of
clarity is he employing, when he says that the notion of analyticity
is insufficiently clear? The answer, not explicit in (Quine, 1951), is
that the standards are those indicated by our discussion in the
previous section; Quine is asking for an explanation which is
acceptable by his naturalistic standards. Such an explanation would
proceed in terms of the way in which language is used, behavioural
terms. It would not presuppose an idea of meaning, and would use such
ideas as definition or convention only in ways which are justified by
the most literal sense of those terms. Second, some responses to
Quine’s position here argue that it has obviously absurd
consequences, such as that meaningful discourse would be impossible or
that we could not understand our language. (See, for example, Grice
and Strawson, 1956.) But Quine’s scepticism
about meanings does not lead to any scepticism
about meaningfulness. If we think of meaningfulness as a
matter of having a meaning then we may think that our words
cannot be meaningful unless there are meanings. But such a way of
thinking is, Quine claims, quite misleading. In (Quine 1953), he
offers a rough and ready behavioural account of meaningfulness; it is
clear from the way the account proceeds that the success of something
along those lines would be of no help at all in defining synonymy or
analyticity.

We said above that Quine seeks ‘to cast doubt’ on the
idea of meaning, and on the use of that idea to explain the distinction
between those changes of doctrine which involve a change of meaning and
those which do not, and thus also to explain analyticity. One might
read (Quine 1951) and get the impression that he is not merely casting
doubt but wholly rejecting these ideas. Even there, however, he accepts
that an acceptable definition of analyticity might be given. In later
works, he himself suggests such a definition. A sentence is analytic
for a given native speaker ‘if he learned the truth of the
sentence by learning to use one or more of its words’ (Quine,
1991, 270; see also Quine 1974, 78–80.) It is analytic without
qualification if it is analytic for all native speakers. By this
criterion, obvious sentences such as ‘Bachelors are
unmarried’ will count as analytic. If we think of the set of
analytic sentences as closed under logical consequence, as Quine
suggests, then all first-order logical truths ‘would then perhaps
qualify as analytic’ (Quine, 1991, 270). Along with this,
he comes to accept that certain revisions of belief do involve a change
of meaning, presumably in a sufficiently clear sense of meaning (Quine,
1991, 270).

It might seem as if Quine completely withdraws his earlier criticism
of the analytic-synthetic distinction and thus, presumably, of Logical
Empiricism as a whole. But in fact this is not so. Three features of
Quine’s version of the distinction make this clear. The first is
that it relies on claims about how words are learned, claims which are
in most cases unknowable. Probably we all learned the word
‘bachelor’ in the same way, but, as Quine says, ‘we
don’t in general know how we learned a word’
(1991, 271). So for many sentences it is wholly unclear whether
they are analytic. The second is the scope of Quinean analyticity. The
idea will perhaps (as Quine says) include first-order logic,
but it will not include mathematics; on this count alone, it is clear
that it will not do what Carnap requires of the idea of analyticity.
Third, and perhaps most fundamental, Quine’s version of the
analytic-synthetic distinction is not an epistemological distinction.
Some changes of doctrine involve changes of meaning, others do not. In
Quine’s view, however, this does not mean that the two sorts of
change must have different epistemological bases. To the contrary: as
we saw in 3.1, Quine rejects the Principle of Tolerance and, with it,
the idea that a change of language takes place on a different kind of
epistemological basis from a change of theory within a language. His
acceptance of a limited conception of analyticity does not change this
picture. As he says: “I recognize the notion of analyticity in
its obvious and useful but epistemologically insignificant
applications” (1991, 271; emphasis added).

Quite generally, Quine’s rejection of the Principle of
Tolerance is the deepest aspect of his disagreement with Carnap. Quine
sees all our cognitive endeavours, whether they involve formulating a
new language or making a small-scale theoretical change, as having the
same very general aim of enabling us to deal with the world better; all
such endeavours have the same very general kind of justification,
namely, as contributing to that end. In this picture, there is no basis
for Carnap’s insistence that philosophy is in principle different
from science. Philosophy, as Quine sees it, has no special vantage
point, no special method, no special access to truth. Here we have the
crucial idea of Quine’s naturalism, discussed in the previous
section.

As we saw in section 2, Quine takes the fundamental epistemological
problem to be that of showing how we come to have knowledge of the
world. He seeks an account which is naturalistic in his austere sense,
and thus starts with the idea that we know about the world only from
impacts of various forms of energy on our sensory nerves (see 2.3,
above). How do we get from such impacts to something recognizable as
knowledge of the world? In the words of the title of Quine’s last
monograph: how do we get from stimulus to science?

This question is central for Quine’s scientific naturalism in
general. An answer would show that this world-view can accommodate an
account of human knowledge. If no answer is available, that world-view
is cast in doubt. For these purposes it is perhaps enough if Quine can
sketch an account, compatible with his naturalistic view, of how we
might acquire the knowledge which we take ourselves to have,
whether or not it is correct in detail. (See Quine 1990c, 291.)

Quine treats knowledge as embodied in language. Apart from other
considerations, language-use is observable and thus subject to
scientific inquiry. Quine’s concern with how we might acquire
knowledge thus takes the form of a concern with how we might acquire
cognitive language. His interest here is in epistemology, rather than
in language for its own sake: “I am interested in the flow of
evidence from the triggering of the senses to the pronouncements of
science…. It is these epistemological concerns, and not my
incidental interest in linguistics, that motivate my
speculations” (1990b, 3).

Much of Quine’s work in epistemology is thus a more or less
speculative discussion of how a child might acquire cognitive language.
This genetic project may seem to be a long way from the traditional
concerns of epistemology. Quine claims, however, that the project in
fact affords us the best obtainable insight into the nature of the
evidence for our theories, and into the relation between theory and
evidence: “the evidential relation is virtually enacted, it would
seem, in the learning” (1975c, 74–75).

Central to Quine’s naturalistic account of knowledge is the
idea that all our knowledge is in some way based upon stimulations of
our sensory nerves. For much of our knowledge, the relation is quite
indirect. (This is one way of expressing holism; see 3.1, above.) Most
sentences are not accepted because of a direct relation between the
given sentence and stimulations of nerve endings; the connection goes
via other sentences, and may be quite indirect and remote. But
then there must presumably be some sentences which are directly related
to stimulations. This is the role that observation sentences play in
Quine’s thought. Acts of uttering such sentences, or of assenting
to them when they are uttered by others, are shared responses to
stimulation. (We shall enter some qualifications at the end of this
sub-section.)

Observation sentence are the starting point for our acquisition of
knowledge, the child’s entry into cognitive language. They are
also the sentences which are evidentially basic. What fits them to
play both roles is that they are independent of other parts of our
language and our theory. Hence they can be mastered by a child
otherwise without linguistic competence and they can be known without
presupposing other parts of our theory.

Many philosophers are content to take for granted the idea of
evidentially basic sentences. Quine, however, cannot take that
attitude; he needs to show how we get “from stimulus to
science”. The first step is to show that we can give a purely
naturalistic account of how some linguistic utterances can be directly
tied to the occurrence of stimulations of the sensory nerves, an
account of observation sentences, more or less. Quine expends enormous
labour on this point.

Quine considers acts of assenting to sentences (or dissenting; but I
shall mostly leave that as understood). He focuses, in particular, on
our dispositions to assent to sentences. (We will briefly
consider the idea of a disposition in the next section.) To be an
observation sentence, a sentence must fulfill two criteria. The
individualistic criterion is that a sentence is an observation sentence
for a given person if he or she is disposed to assent to it when (and
only when) he or she is undergoing appropriate sensory
stimulations, regardless of her internal state (e.g. the ancillary
information which he or she possesses). “It’s warm in
here” presumably satisfies this criterion; my willingness to
assent to it perhaps depends only on which of my sensory nerves are
stimulated at the given moment. “There’s milk in the
refrigerator” presumably does not; unless I am actually looking
into the refrigerator at the time, my willingness to assent to it
depends not on what I am experiencing at the time but on my internal
state, what I remember. The social criterion is that the
individualistic criterion hold across the linguistic community as a
whole. To specify this more precisely is tricky, and I shall postpone
the matter for a few paragraphs.

Even the individualistic criterion raises considerable complications
and difficulties. We speak of a disposition to assent (or dissent) in
response to a pattern of stimulation but this is not quite accurate.
Such a pattern, a complete list of which sensory nerves are firing, and
in which order, will hardly ever repeat itself. So what we need is,
rather, the idea of a correlation of a response with a type of
stimulation
pattern[1].
But the relevant idea of a type here is complicated. The physical
resemblance of two stimulation patterns, what Quine calls receptual
similarity, is not enough to make them constitute events of the
same type, in the relevant sense; two such patterns may resemble each
other very closely yet lead to quite different responses. (Two
occasions on which I am driving a car may be almost identical in terms
of my stimulation patterns, except that on one occasion I see a red
light and on the other I see a green light. As far as my reaction goes,
that small difference outweighs all the similarities.) What is wanted
is a more complex notion which Quine calls perceptual
similarity. Very roughly, two stimulation patterns count as
similar (for an animal, at a time) if they tend to lead to the
same
response[2].

With the account of perceptual similarity in place, we can say what
it is for a sentence to be observational for me: if I am disposed to
assent to it on one occasion on which I have a certain neural intake,
then I will also be disposed to assent to it on any other occasion on
which I have neural intake which is (sufficiently) perceptually
similar.

It is worth emphasizing the fact that the definition of the key
notion of perceptual similarity is behavioural. It avoids any idea of
experience, of awareness, of what strikes the person (or other animal)
as more similar to what. It is simply a matter of responses. This is in
accord with Quine’s insistence on what he takes to be scientific
standards of clarity and rigour. One consequence of it is that the
notion cannot be invoked to explain behaviour. Quine is under
no illusions on this score. (See 1975b, 167, where the point is
explicit.) The behavioural account does not explain our
understanding of observation sentences; explanation, if possible at
all, comes at the neuro-physiological level. What the behavioural
account does is to make it clear exactly what behaviour constitutes
that understanding and, hence, what the neuro-physiological account
would have to explain. (It also shows that there is indeed
something to be explained.)

So far we have only an account of what it is for a sentence to be an
observation sentence for a particular person. But our language is
shared, so we need to generalize the criterion across the linguistic
community. One might at first think that the social criterion would be:
if one person is disposed to assent to the sentence on any occasion on
which they have a certain neural intake, then any other person having
the same neural intake will also be disposed to assent to it. Quine
gives essentially this account in (1960). As he quickly comes to see,
however, it is not tenable, for it assumes that we can make sense of
the idea of “same neural intake” between different people.
But different people have different sensory nerves.

Quine returned to this problem on and off over the next thirty-five
years. His eventual solution is that a sentence only counts as an
observation sentence if an occasion which leads to my having neural
intake which disposes me to assent to it also leads to your having
neural intake which disposes you to assent to it. Here there is no
cross-person identification of neural intake or cross-person standards
of perceptual similarity. The solution does, however, require that our
standards of perceptual similarity line up in the right sort of way.
Two occasions which produce in me neural intakes which are perceptually
similar by my standards must also (often enough) produce in you neural
intakes which are perceptually similar by your standards. Quine is
happy enough with this assumption of mutual attunement and suggests
that it can be explained along evolutionary lines (see 1996,
160f.).

We have been explaining what is involved in our having shared
responses to stimulation. For the most part, Quine assumes that assent
to an observation sentence simply is such a response. This assumption,
however, cannot be quite correct. It may look for all the world as if
there were a rabbit in front of me, even though there is not. If
I have no reason to be suspicious I will be disposed to assent to
“Rabbit?”; if I know about the deception, however, I will
not be. So my disposition to assent does not, after all, depend solely
on my sensory stimulations at the time. It depends also on my internal
state, whether I know that in this case the rabbit-like appearance is
misleading. The difficulty arises from the corrigibility of
“There’s a rabbit”, a feature which, on most
accounts, it shares with just about every sentence other than those
about the speaker’s current experience. If a sentence is
corrigible then there will be circumstances in which it is false even
though they will produce in observers stimulation patterns which would
generally lead them to assent to it. But then some observers may know
that the circumstances are of this deceptive kind and not be disposed
to assent, while others have no such knowledge and are disposed to
assent. The moral of this is that assent, even to observation
sentences, is not a mere response to stimulation; the responder’s
internal state (their having ancillary knowledge, or not) may also play
a role.

Quine does not seem to have fully appreciated this point, though
some of his later discussions come close to doing so (see, in
particular, Quine 1996). It is not fatal to his general account; it
complicates the story rather than requiring a radical change. There may
be no sentences which can be wholly mastered simply by acquiring
appropriate dispositions to assent and dissent in response to current
stimulations. But for some sentences acquiring such dispositions comes
close to mastering their use, because those sentences are almost
always true in those cases where observers receive sensory
stimulations which dispose them to assent. (Clearly this will be a
matter of degree.) So the acquisition of the relevant dispositions, and
partial mastery of the sentence, can be used as a basis on which the
child can learn more of the language, and more about the world. This
further learning in turn allows the child to modify her or his original
disposition to assent and dissent merely in response to current
stimulation.

To this point, our focus has been on observation sentences.
Quine’s treatment of more sophisticated parts of language is
notably sketchier and more speculative than his detailed discussion of
observation sentences. In part this may be because he holds that it is
most important to understand the very first step into cognitive
language, how such language is possible at all. It may also be that the
difficulty in getting a satisfactory account of observation sentences
impeded him.

Beyond these points, there is, from a Quinean perspective, a limit
to how detailed an account we should expect to have of the acquisition
of sophisticated cognitive language. Mastery of an observation sentence
corresponds (more or less) to a relatively straightforward disposition:
to assent when receiving a stimulation pattern within a certain range.
For most sentences, however, this is not the case. What disposition
must one have acquired in order to count as understanding a sentence
such as “The economy is in recession”? Perhaps one must be
able to give evidence if pressed, but what counts as evidence is almost
unmanageably diffuse; what evidence one actually has will vary greatly
from one person to another. One’s assent to the sentence is no
doubt tied to sensory stimulations that one has received, if only the
sight of those words in a newspaper. These links, however, are
“multifarious [and] not easily reconstructed even in
conjecture” (1960, 11). A relatively clear-cut account of the
sort that Quine gives of observation sentences is simply not
available.

So Quine does not offer any sort of detailed account of the
acquisition cognitive language beyond the observation sentences.
Instead, he considers stages on the way, forms of language which one
might suppose could be easily acquired by a child who has mastered
observation sentences and which might provide steps leading to yet more
advanced language.

One such step, which is emphasized in Quine’s later work, is
the mastery of what he calls observation categoricals. These
are sentences of the form “Whenever X happens,
Y happens”, where the variables are to be replaced by
observation sentences. (E.g. “Whenever there’s smoke,
there’s fire.”) It is plausible to suppose that a child who
has learnt the observation sentences can come by a mastery of the
relevant observation categorical. The observation sentences are what
Quine calls occasion sentences, true on some occasions and
false on others, whereas the observation categoricals are eternal
sentences, true or false once for all. Quine suggests that we can
think of observation categoricals as a plausible first step into
mastering eternal sentences, which make up our serious theoretical
knowledge.

Another step of the same kind is what Quine calls eternal
predications, subject-predicate sentences true or false once for
all, such as “Fido is a dog”. Assuming the child has learnt
both terms as observation sentences, the sight of the dog will dispose
him to assent to each. Quine speculates that the sound of the word
“Fido” may have something of the same effect as the sight
of the beast, inclining our learner to assent to “Dog” and
thus to “Fido is a dog”. It is notable that there is a sort
of use-mention confusion operating here, if Quine’s suggestion is
correct. Language is learned by confusion and “short leaps of
analogy” rather than by “continuous derivation”
(1975c, 178–9); indeed a holistic language cannot be learnt without
such leaps.

A further advance, in Quine’s view, takes place when the child
comes to use similar sentences but with two general terms, such as
“Dogs are animals”. Such a sentence, Quine remarks is
‘‘really a universal categorical, ‘Every α is a
β’.’’ (1974, 66). This kind of sentence, can be
represented using pronouns (“If something is a dog then
it is an animal”) or, more or less equivalently, using
the logical device of quantifiers and variables. Such sentences have a
particular importance for Quine in connection with the idea of
reference. Merely to be able to use a name, to be able to name
Fido upon seeing him, for example, is not yet to refer; one might
simply be using the term as a response to the sight of the beast, hence
as an observation sentence. Reference, as Quine sees the matter,
requires the capacity to reidentify the object over time and changing
circumstances: if a dog is barking then it—that very
same dog—is hungry; hence the importance of pronouns.

Quine also has things to say on more familiar epistemological
themes. In some cases he indicates how they can be integrated into his
approach; thus he suggests that we can (albeit unrealistically)
schematize the testing of a scientific theory by thinking of ourselves
as deriving observation categoricals which can then be directly tested
against observation sentences. In other cases he is content to adopt
more or less unchanged the account given by earlier authors, as in his
list of the virtues of a theory (see 1990a, 20). My account above has
stressed the most novel parts of his epistemology.

One issue left unaddressed above is the question whether
Quine’s naturalized version of epistemology is normative. Some
commentators have claimed that it is not, and that this is a serious
defect (see Kim, 1988). Others defend Quine, claiming that naturalized
epistemology is normative (see Gregory, 2008). Quine himself has
weighed in, saying that critics ‘are wrong in protesting that the
normative element…goes by the board’ (Quine, 1990, 19). He
cites the ‘finding of natural science…that our information
about the world comes only through impacts on our sensory
receptors’ (Quine, 1990, 19) as being normative, ‘warning
us against telepaths and soothsayers’ (Quine, 1990, 19). More
generally, naturalized epistemology is concerned with ‘the whole
strategy of rational conjecture in the framing of scientific
hypotheses’ (Quine, 1990, 20). Naturalized epistemology is thus
certainly normative in this sense: it tells us that in drawing up
scientific theories, we should rely on the evidence of the
senses rather than on soothsayers, we should aim at simple
theories, and so on. In telling us these things, however, it relies on
what we already know: it deploys some parts of our science to guide
attempts in other areas. It does not take a normative attitude towards
science as a whole, criticizing or justifying it by wholly external,
non-scientific standards. That would require a wholly extra-scientific
position, an idea which Quine derogates as ‘First
Philosophy’ (e.g. Quine 1981, 67). The rejection of any such idea
is one way of phrasing the naturalism he advocates.

Quine takes seriously the idea that “it is within science
itself, and not in some prior philosophy, that reality is to be
identified and described” (1981, 21). A consequence is that our
best theory of the world tells us as much as we know about reality.
(Our best theory at given time tells us as much as we know at that
time; no doubt our views will progress.) So setting out the broad
outlines of that theory is the Quinean version or analogue of
metaphysics, though he does not much use the word. This subject
interacts with that of the last section: Quine’s account of the
world lays down the constraints within which an account of knowledge
must proceed, and also is the knowledge that must be accounted
for.

How does Quine think we should establish the sort of claims that we
are calling “metaphysical”? Some points are familiar from
our discussion in section 2. First, we do not resort to any special
kind of philosophical insight; we rely upon our ordinary knowledge.
Second, what matters is ordinary knowledge as refined and improved
upon: science. Third, we rely upon the idea of regimented theory,
science formulated in a language that is clarified and simplified
“beyond what might reasonably be urged upon the practicing
scientist” (1957, 235; see 2.4, above). A further point is that
in striving for the clarity and simplicity of our theory we must
consider the whole theory; local gains may be offset by global losses.
It is thus to overall regimented theory that we look when we are
“liming the true and ultimate structure of reality” (1960,
221).

In some cases, the answers that Quine gives to such questions are,
as we shall see, quite different from what unreflective common sense
(or ‘intuition’) might suggest. What is Quine’s
justification for relying on the idea of regimented theory, rather than
on our ordinary conceptual scheme? (Cf. Strawson, 1959, Introduction.)
Part of the answer here is that science is in the same line of business
as ordinary knowledge but does it better. But part of the answer
is the idea that “our ordinary conceptual scheme” does not
pick out anything definite enough to answer metaphysical questions.
Thus Quine says: “…a fenced ontology is just not implicit
in ordinary language…. Ontological concern is not a correction
of a lay thought and practice; it is foreign to the lay culture, though
an outgrowth of it” (1981, 9).

Regimentation, in Quine’s view, involves paraphrase into
logical notation. Such paraphrase greatly clarifies and simplifies our
theory. Inferences which are a matter of logic will be revealed as
such; where additional assumptions are required it will be explicit
just what is needed. The logic which Quine takes as the structure of
regimented theory is classical (bivalent) first-order logic with
identity. Bivalence is justified on the grounds of simplicity. It is
not that we have some independent insight into the nature of the world
which shows us that every sentence of regimented theory is either true
or false. It is, rather, that the simplicity that we gain from making
this assumption, justifies our using a bivalent language; the
metaphysical claim follows along. (This reversal of direction should
remind us of Carnap. The difference is that Quine does not accept the
Principle of Tolerance; see section 3, above.)

Quine’s choice of first-order logic, rather than second-order
logic, has been more controversial than his adoption of bivalence. One
reason he gives for the decision is that every formalization of
second-order logic (unlike first-order logic) is incomplete, relative
to the standard semantics. A further reason is that one purpose of the
canonical framework is to enable us to assess the ontology of a theory.
From this point of view it is an advantage that first-order logic has
no ontological presuppositions of its own. (By adopting that logic we
do commit ourselves to there being some object or other, but not to the
existence of any particular entity.) Here again there is a clear
contrast with second-order logic, which does have ontological
presuppositions. Exactly what those presuppositions are is unclear and
has been debated; for Quine, this unclarity is a further reason to
avoid the subject entirely.

Paraphrasing a theory into classical logic imposes extensionality on
it: a predicate may be replaced by a co-extensive predicate without
change of truth-value of the containing sentence; likewise an embedded
sentence by a sentence of the same
truth-value[3].
Extensionality imposes quite severe
restrictions. It requires, for example, that attributions of belief,
and other propositional attitudes, be regimented into a form quite
different from that which they may appear to have. So one might suppose
that Quine accepts extensionality reluctantly, as the price to be paid
for the advantages of the use of logic in regimenting theory. Such is
not his attitude, however. To the contrary, he thinks of the clarity
that extensionality brings as a great advantage, and of theories that
lack it as not fully comprehensible: “I find extensionality
necessary, indeed, though not sufficient, for my full understanding of
a theory” (1995, 90f.)

Quine’s regimented theory, then, is the sum total of our
knowledge, the best that we have, reformulated so as to fit into the
framework of first-order logic. Besides the truth-functions,
quantifiers, and variables of logic, the vocabulary consists only of
extra-logical predicates. All metaphysical questions can thus be boiled
down to two: What objects do the variables range over? and: What sorts
of primitive predicates are to be admitted?

To the first of these questions Quine offers a straightforward answer:
his ontology consists of physical objects and sets. He counts as a
physical object the matter occupying any portion of space-time,
however scattered the portion and however miscellaneous the occupants;
such an object need not be what he calls a “body”, such as
a person or a tree or a building (see 1981, 13). He briefly entertains
the idea that we could manage without postulating matter at all,
simply using the sets of space-time points, where these are understood
as sets of quadruples of real numbers, relative to some co-ordinate
system, an ontology of abstract objects only (see Quine, 1976). He
seems to see no knock-down argument against this but abandons it,
perhaps because the gain is too small to justify the magnitude of the
departure from our ordinary views. That he is willing to consider such
a view, and take it seriously, shows something about his general
attitude.

Regimented theory contains no abstract objects other than sets. Many
abstracta, however, can be defined in terms of sets: numbers,
functions, and other mathematical entities being the most obvious.
Quine excludes other alleged abstracta, such as propositions,
and possible entities,. The chief reason for this is that he finds the
identity-criteria for such entities unclear. He holds, quite generally,
that we should not postulate entities without having clear
identity-criteria for them. (This is the view that he sums up in the
slogan “no entity without identity”; see (1969, 23) and
elsewhere.) Doing so would threaten the clarity and definiteness which
the notion of identity brings to theory; local gains from postulating
propositions are not worth this global loss.

Regimented theory also has no place for mental entities, most
obviously minds, if those are taken to be distinct from physical
entities. The qualification is important. Many mental entities can be
admitted as special cases of physical objects. Thus my act of thinking
about Fermat’s Last Theorem at a particular time can simply be
identified with my body during that period of time (see 1995, 87f.).
The things that we might want to say about my act of thinking (that it
was inspired, or stupid, or what have you) can simply be reconstrued as
predicates true or false of physical objects. This is the view
sometimes known as anomalous monism or as token-token identity theory,
as distinct from type-type identity theory. I may think of the theorem
at many times, over the years, and on each occasion that act is
identified with the physical state that I am in at the time.
Token-token identity theory does not claim that these physical states
have anything in particular in common, still less that all acts of
thinking about the theorem have something in common. There is no claim
that each act of thinking about the theorem can be identified with,
e.g. a repeatable pattern of the firing of brain cells. It is enough
for Quine’s purposes that each particular act of thinking can be
identified with a physical object. This ontological physicalism might
seem almost trivial; Quine speaks of it as “[e]ffortless monism
… form without substance” (1995, 85). (Note that this view
excludes disembodied minds and mental entities. Quine thinks
that is no loss at all. Note also that it can be construed either as
eliminating mental entities or simply as identifying
them with physical objects. Quine prefers the latter phrasing but
thinks there is no real difference here; cf. 1960, 265.)

On the issue of the admissibility of predicates, Quine’s
physicalism is more complicated. The requirement here is that the
difference between a predicate’s being true of a given object
and its being false of it should, in all cases, be a physical
difference: “nothing happens in the world, not the flutter of an
eyelid, not the flicker of a thought, without some redistribution of
microphysical states…. physics can settle for nothing
less” (1981, 98). If a predicate such as “…is
thinking about Fermat’s Last Theorem” picks out genuine
events in the world then there is a physical difference between its
being true of a person and its not being true of them: a fact of the
matter.

A difficulty in making sense of this is that the idea of a
physical fact is not one that we can definitively specify. To
tie the idea too closely to current physics would rule out fundamental
changes in that subject; to leave it floating free might seem to allow
anything to count. But clearly Quine does not mean just any subject
that someone might call by the name “Physics”. He has in
mind a subject continuous with our physics, alike or superior in its
coherence and in its explanatory power. (In particular, it would not
have “an irreducibly psychological annex”; see 1986a, 403f.).
If phenomena occurred which could not be explained by any theory of
that kind, then Quine’s physicalism would go by the
board.

The most controversial application of this view is to (alleged)
mental phenomena. Within that realm, Quine focuses on attributions of
propositional attitudes, statements that so-and-so believes that
such-and-such, or hopes that, or fears that, etc. (One reason for this
focus may be that his interest is primarily in human knowledge; another
that some other mental states, such as pain, can perhaps be accounted
for by identifying them with certain types of neurophysiological
events.)

On the face of it, ascriptions of belief (to stick to that case)
violate extensionality. If Mary is the Dean, still Tom’s
believing that the Dean sings well is not the same as his believing
that Mary sings well, since her accession to the Deanship may be
unknown to him. Quine escapes this sort of problem by taking an
attribution of belief to express a relation between the believer and a
sentence, understood to be, in the usual case, in the language
of the ascriber (not the language of the believer, where the languages
differ).

It is worth noting the idea of another sense of belief-ascription
which would not be vulnerable even prima facie problems of
extensionality: so-called de re belief, as distinct from
de dicto belief. In the 1950s Quine argued that there must be
such a sense. In the late 1960s, however, he abandoned the idea, for
lack of clear standards of when it is correct to ascribe a de
re belief to someone. (See Quine, 1956 for a statement of the
distinction, and Quine, 1973 for retraction.) Other philosophers,
however, continue to hold the idea.

Construing attributions of belief as statements of attitudes towards
sentences gives them a syntax and an ontology that Quine can accept.
That does not mean, however, that the idiom “A believes
that p” satisfies his physicalistic criterion, i.e. that
all statements of this form correspond to (physical) facts. The matter
is complicated. Quine certainly accepts that most uses of this idiom
do correspond to facts. The relevant facts are
neurophysiological states of the person concerned, and those states are
causally connected with actions which the person performs, or would
perform under certain circumstances, and which we count as
manifestations of the belief, or lack of belief. (Assenting or
dissenting if one were asked is one such action, but only one among a
myriad.) In cases where we have evidence for or against the ascription
of a belief, the evidence consists in behaviour and there is presumably
one or more neurophysiological states which explain the behaviour. The
person’s being in those states, although not specifiable in
neurophysiological terms, is the among the physical facts in which the
truth of the ascription consists. Even where there is no behaviour of
the relevant kind, there may still be dispositions to behave in those
ways under certain unrealized circumstances. Here the dispositions are
physical states in which the truth of the ascription consists. So in
most cases where we ascribe belief, there is a fact of the matter which
makes the ascription true or false. (For some discussion of
dispositions, see a few paragraphs hence.)

The belief idiom, however, also lends itself to use in other cases,
where there is no fact of the matter. These are not merely cases in
which we have no evidence. They are case in which no behavioural tests
which we might have carried out would have supplied evidence, cases in
which there simply is nothing in the subject’s neurophysiology,
and hence nothing in their actual or potential behaviour, which would
decide the matter. Quine puts the point like this:

Some beliefs, perhaps belief in the essential nobility
of man qua man, are… not readily distinguishable from mere lip
service, and in such cases there is no fact of the matter…. But
most attributions or confessions of belief do make sense…. The
states of belief, where real, are… states of nerves.
(1986a, 429)

Quine explicitly acknowledges that we could not in practice manage
without idioms of propositional attitude, and that most uses of such
idioms are entirely unobjectionable. But since such idioms allow the
formation of sentence which do not correspond to facts of the matter,
they are not part of regimented theory and should not be used when we
are concerned with “limning the true and ultimate structure of
reality” (1960, 221). (Some philosophers might insist:
‘Either you accept the concept of belief or you
don’t’; Quine would not agree.)

A somewhat similar point can be made about subjunctive or
counterfactual conditionals. Some are factual, but the general
counterfactual idiom conditionals allows for the formation of sentences
which are not factual. Like propositional attitudes, counterfactual
conditionals have an important role in our practical lives. They are
also closely connected with dispositions which, as we have seen, play a
central role in Quine’s account of language and how it is
learned. The connection is easily seen: to call an object fragile is to
say that it would break if it were dropped onto a
hard surface from a significant height.

Quine does not accept the general counterfactual idiom, “if
X were to happen then Y would happen”, as part
of regimented theory. As in the case of belief, the unrestricted use of
this idiom allows us to form sentences whose truth-conditions are, at
best, unclear. A famous example is the pair, presumably alluding to the
Korean war of the early 1950s: “If Caesar were in charge he would
use the atom bomb”; “If Caesar were in charge he would use
catapults” (see Quine, 1960, 222. In such cases, we have no
reason to think that some (physical) fact is being claimed. Many
dispositions, however, are perfectly acceptable by Quinean standards.
To call the glass fragile is to attribute to it a structure which would
lead its breaking if it were dropped from a significant height onto a
hard surface; the structure is a physical state, even if we cannot
specify it in physical terms.

Quine claims that the dispositions he relies on in his account of
language are like the case of fragility rather than the case of Caesar.
The disposition to assent to an observation sentence when receiving
certain stimulations is a physical state of the person concerned, in
particular, presumably, of his or her brain. The claim that a given
person has such a disposition is thus a claim about the state of a
physical object. It is, moreover, a claim that we can test, at least
under favourable conditions. There is no reason to exclude it from
regimented theory.

Another idiom which Quine famously excludes from regimented theory
is that of modality, statements that such-and-such must be the
case, or cannot be the case, and so on. Such idioms have been
the subject of much discussion on the part of Quine and (especially)
his critics; the discussion here will be very brief. Technically, there
are similarities with the case of belief. There is prima facie
violation of extensionality which can, however, be avoided by taking
necessity to apply to sentences; some philosophers have claimed that
there is a de re sense of necessity which does not lead to
even prima facie violations of extensionality. Quine’s
attitude towards modality, however, is far less sympathetic than his
attitude towards belief; he is particularly unsympathetic towards the
idea of de re necessity, which he sees as requiring
“Aristotelian essentialism” (Quine, 1953, 155).

What frames these critical points is the fact that Quine holds that
regimented theory, the best and most objective statement of our
knowledge, simply has no need for a notion of necessity. The benefit of
including such idioms in regimented theory is not worth the cost in
unclarity that it would bring.

Truth, in Quine’s view, is immanent. In accord with his
fundamental naturalism, he sees judgments of truth as made from within
our theory of the world. For this reason, he is in sympathy with what
is sometimes called disquotational theory of truth: to say that a
sentence is true is, in effect, to assert the sentence. Two
qualifications must be made. First, the disquotational view is not a
definition of “is true”. It enables us to
eliminate the predicate when it is applied to a finite number of
specific sentences but not from contexts where it is applied to
infinitely many. Such contexts are of particular importance to logical
theory. We say, for example, that a conjunction is true just in case
both conjuncts are true; here “is true” cannot be
eliminated. Second, calling a sentence true is in one way unlike
asserting it. If we subsequently change our verdict on it we say that
we used to believe it but now we don’t. We do not, however, say
that it used to be true but now it isn’t; rather we say that it
was never true. Quine, however, sees this as simply a point of usage,
with no particular philosophical implications.

The immanence of truth, on Quine’s account, might suggest that
his realism is threatened by what has become known as the
underdetermination of theory by evidence: that two or more rival
theories might have all the same observational consequences, and thus
be empirically equivalent. Quine finds underdetermination harder to
make sense of than might appear and, in any case, does not see a threat
to realism; I shall defer further discussion to the next section.

In this section we take up two ideas much discussed by commentators.
Neither is essential for an understanding of Quine’s overall
philosophy, although in each case, but especially in the case of
indeterminacy, the opposite claim has been made. (See Ebbs, 1997; for a
defense of the position taken here, see Hylton, 2007.)

The basic idea of underdetermination is stated at the end of the
previous section. In Quine’s idealized schematization of the
relation between theory and evidence, evidence for theory consists of
observation categoricals. (These latter can, in turn, be tested by
observing or contriving situations in which relevant observation
sentences are true.) The case which most obviously poses a potential
threat to realism is that of a final global theory, a perfected and
completed version of our own. What if there are two or more such
theories, each of which implies all true observation
categoricals, and which possess other theoretical virtues, such as
simplicity, to an equal degree? (Note that the theory will not be
implied by all the true observation categoricals; apart from
other considerations, some sentences of the theory will essentially
contain terms which do not occur in observation categoricals.)

Quine is often thought to accept underdetermination. But in fact he
holds that there is considerable difficulty in making sense of the
doctrine. He identifies theories with sets of sentences, not with sets
of sentence-meanings (propositions). So we can quite trivially obtain
an empirically equivalent alternative to any theory: simply spell one
of the theoretical terms differently at every occurrence. The result is
a different set of sentences which imply all the same observation
categoricals. The difference from the original theory, however, is
merely orthographic; this possibility is clearly not of any
philosophical significance.

A closely related point can be made in terms of translation.
Translation of observation categoricals is, presumably,
unproblematic in principle. So we can count two theories as empirically
equivalent not merely if they imply the same observation categoricals
but also if they imply intertranslateable observation categoricals. In
that sense, however, the theory we are postulating is empirically
equivalent to its translation into any other language. But this is also
not of any great philosophical significance.

A version of underdetermination that might threaten realism would
thus assert that our postulated complete global theory of the world
will have empirically equivalent alternatives with no translation from
one to the other being possible, i.e. that we cannot obtain one from
the other by reconstruing the predicates of the theory. Quine comments:
“This, for me, is an open question” (1975a, 327). Much of
his subsequent discussion of underdetermination takes place in terms of
the weaker idea that our theory might have empirically equivalent
alternatives such that “we would see no way of
reconciling [them] by reconstrual of predicates” (loc.
cit, emphasis added; cf. also 1990, 97).

If some version of underdetermination were true, how should we
respond? This is an issue on which Quine not merely changed his mind
but vacillated, going back and forth between what he calls the
“sectarian” and the “ecumenical” responses. The
sectarian response is to say that we should not let the existence of
the alternative in any way affect our attitude towards our own theory;
we should continue to take it seriously, as telling us the unique
truth about the world. (We are assuming that the two theories possess
all theoretical virtues to equal degree; clearly Quine would say that
if one theory were superior in some way then we would have reason to
adopt it.) The ecumenical response, by contrast, counts both theories
as true. In almost his last word on the subject he suggests that there
may be little at stake since the “fantasy of irresolubly rival
systems of the world” takes us “out beyond where linguistic
usage has been crystallized by use” (1990, 100f). In an even
later piece of writing, however, Quine speaks of himself as
“settled into the sectarian [attitude]” (1986b, 684f.).

Quine can afford to vacillate because, in his view, nothing very
much turns on the issue. In particular, he never holds that
underdetermination, in any version, would threaten realism; at no time
does he suggest that it casts doubt on the truth of our theory. That is
not what is in question between the sectarian and the ecumenical
positions; all that is in question is whether the alternative theory
should also be counted as true. Nor is this surprising. The
terms in which underdetermination is stated, such as observation
categoricals, are part of our theory, as would be the demonstration
that another theory was empirically equivalent. The point here is the
naturalism which we have emphasized throughout. Nothing in our
epistemology pronounces on the status of theory from an independent
standpoint; to the contrary: it presupposes the truth of our theory.
This central idea is not cast in doubt by underdetermination.

The general claim of the indeterminacy of translation is that there
might be different ways of translating a language which are equally
correct but which are not mere stylistic variants. The claim includes
what one might think of as the limiting case of translation, that in
which a given language is ‘translated’ into itself.

Some philosophers hold that the idea of indeterminacy is absurd, or
that it amounts to an extreme form of scepticism about whether we ever
understand one another, or whether correct translation is possible at
all. It is not hard to see how such opinions arise. One picture of
communication is like this: you have an idea, a determinate meaning, in
your mind and convey it to me by your utterance. To those who have that
picture, indeterminacy threatens the whole idea of communication, for
it suggests that the conveying is always vulnerable to drastic
failure. In the case of translation, the analogous view is that
synonymy, or sameness of meaning, is the criterion of correct
translation; in that case, indeterminacy may appear as a denial that
translation is possible at all.

Such views, however, take for granted a view of communication, or of
translation, which is very far from Quine’s. For Quine, the
criterion of successful communication, whether or not it involves
translation, is fluent interaction, verbal and nonverbal:
“Success in communication is judged by smoothness of
conversation, by frequent predictability of verbal and nonverbal
reactions, and by coherence and plausibility of native
testimony” (1990, 43). From this point of view, talk of synonymy
and of ideas in the mind is simply a theoretical gloss which is (at
best) in need of justification. Quine doubts that the gloss is
justifiable; scepticism about the theorizing, however, is not
scepticism about the data. Smooth communication certainly occurs,
sometimes in cases where different languages are involved. That
successful translation occurs is not cast in doubt by anything he says;
his claim, indeed, is that it may be possible in more than one way.

At this point we need to distinguish two kinds of indeterminacy.
Quine introduces the general idea of indeterminacy, in Chapter Two of
(1960), without explicitly distinguishing them, but subsequently comes
to treat them quite differently. The first is indeterminacy of
reference: some sentences can be translated in more than one way,
and the various versions differ in the reference that they attribute to
parts of the sentence, but not in the overall net import that they
attribute to the sentence as a whole. (This doctrine is also known as
“ontological relativity” and “inscrutability of
reference”.) To use an example which has become famous, a given
sentence might be translated as “There’s a rabbit” or
as “Rabbithood is manifesting itself there” or as
“There are undetached rabbit parts”, or in other ways
limited only by one’s ingenuity. All that is needed is what Quine
calls a proxy function, which maps each object onto another object and
each predicate onto one which is true of a given proxy-object if and
only if the original predicate is true of the original object. For
terms referring to physical objects, he suggests, we can take the
proxy-function to map each object onto its space-time complement. The
change to the translation of singular terms and the change to the
translation of predicates cancel out, leaving the overall significance
of the sentence unchanged. (Note that it will not help to ask the
person we are translating whether she means to refer to the family dog
or to its space-time complement: her answer is subject to the same
indeterminacy.)

Indeterminacy of reference is akin to a view of theoretical entities
put forward by Ramsey: that there is no more to such an entity than
the role that it plays in the structure of the relevant theory (see
Ramsey, 1931). For Quine, however, the point holds for all objects,
since he “see[s] all objects as theoretical… . Even our
most primordial objects, bodies, are already theoretical” (1981,
20). Quine holds, moreover, that that considerations akin to those of
the previous paragraph amount to a “trivial proof” of
indeterminacy of reference (1986c, 728).

The second kind of indeterminacy, which Quine sometimes refers to as
holophrastic indeterminacy, is another matter. Here the claim
is that there is more than one correct method of translating sentences
where the two translations of a given sentence differ not merely in the
meanings attributed to the sub-sentential parts of speech but also in
the net import of the whole sentence. This claim involves the whole
language, so there are no examples, except perhaps of an exceedingly
artificial kind. There is also nothing resembling a proof; in some late
works, indeed, Quine refers to it as a “conjecture”
(loc. cit.). At some earlier points, he seems to think that
sufficiently clear-headed reflection on what goes into translation will
suffice to make the idea at least plausible. All that can be required
of a method of translation is that it enables us to get along with the
speakers of the other language: why should there not be more
than one way to do it?

Arguments have been offered for holophrastic indeterminacy based on
the idea of underdetermination of theory by evidence. Perhaps
there is determinate translation of observation sentences, and thus
observation categoricals. Still, if two distinct theories are
compatible with all truths stated in observational terms, surely we
could plausibly attribute either theory to the speaker of the other
language? The weakness of this kind of argument is that translation
must presumably preserve more than links between sentences and
stimulations, as captured by observation sentences; it must also
preserve links among sentences, links which make it more or less likely
that a person who accepts a given sentence will also accept another.
Could be methods of translation which preserved both kinds of links but
nevertheless yielded different results? Quine’s term
“conjecture” seems apt.

Given the interpretation advanced in section 3, above, indeterminacy
is not crucial for Quine’s rejection of the sort of use that
Carnap makes of the idea of analyticity. He has other arguments on
that score, as we saw. More generally, indeterminacy is not a crucial
part of Quine’s overall view. (His coming to speak of it as
conjectural, while not questioning other parts of his philosophy,
suggests that this is his view.) If we were sure that translation is
determinate, we could perhaps use the idea to define a notion of
synonymy. (Agnosticism here favours the contrary position.) And, as
Quine has indicated, we could then define the meaning of an expression
as the set of synonymous expressions. Such a notion of meaning might
make some difference. It might, for example, provide a criterion of
identity which enabled us to accept beliefs as entities (though it
also might not: the criteria of individuation of meanings given by our
hypothesized notion of synonymy might be too fine or too coarse to
serve as a criterion of belief-identity). It will not, however, play
the most important roles in which philosophers have cast the idea of
meaning. In particular, it will not play a role in the explanation of
how we understand our language, or of how communication is
possible.

In the 1930s and 1940s, many scientifically-oriented philosophers
tended to assume some form of Logical Empiricism. One important aspect
of Quine’s influence on the course of philosophy is that he
called that view or nexus of views into question (see section 3,
above). Some of his criticisms are detailed and technical. His target,
however, was not a detail but the fundamental ideas of Logical
Empiricism, that there is a distinction between analytic truths and
synthetic truths which can account for a priori truth. After
Quine’s work of the early 1950s, philosophers, even those who did
not accept his detailed arguments could no longer take it for granted
that some form of Logical Empiricism is correct. This was a very major
change.

Quine’s rejection of Logical Empiricism him leads to two
(connected) views which have been extremely influential. First, he
rejects the idea of a distinction between philosophy on the one hand
and empirical science on the other hand. To the contrary: he sees
philosophy as essentially in the same line of work as science, but
mostly concerned with more theoretical and abstract questions. This is
an integral part of his naturalism. Second, his criticism of Carnap
opens the way for something that might be called metaphysics: for very
general reflections on the nature of the world, based on the best
scientific knowledge that we have and on claims about how that
knowledge might be organized so as to maximize its objectivity and
clarity.

Both of these Quinean views, his naturalism and his acceptance of
something like metaphysics, correspond to very important developments
within analytic philosophy over the past half-century. We cannot know
to what extent these developments would have taken place even without
Quine’s work; it is, however, hard to resist the idea that his
influence has at least played a significant role. (In the case of
metaphysics, in particular, it is notable that two leading figures,
Saul Kripke and David Lewis, were students of Quine’s.) For the
most part, however, those doctrines have taken on forms that Quine
himself would be strongly opposed to.

In the case of naturalism, many philosophers have welcomed the idea
that they are free to use concepts and results drawn from empirical
science. Fewer have accepted that philosophy should also be constrained
by scientific standards of clarity, of evidence, and of
explanatoriness. The result is that while views which claim to accept
naturalism are common, those which accept Quine’s standards of
what counts as reputable naturalistic philosophy are not.

The case of metaphysics is similar but perhaps more extreme. Quine
does accept that the philosopher is in a position to make very general
claims about the world (that there are sets but not properties, for
example). In his hands, such claims are answerable to the idea of a
total system of our scientific knowledge, regimented so as to
maximize clarity and system. Many philosophers have welcomed the
freedom to speculate about the nature of the world but have not
accepted Quine’s constraints on the process. The result is a
flourishing of metaphysics, often based on ordinary (unregimented)
language or on the alleged deliverances of ‘intuition’;
much of this work would be anathema to Quine.

On the one hand, then, Quine’s work has been extremely
influential and has done much to shape the course of philosophy in the
second-half of the twentieth century and into the twenty-first. On the
other hand, much of the work directly or indirectly influenced by Quine
is of a sort that he would have thought quite misguided.

See the link in the Other Internet Resources to the list of
writings of Quine compiled by Eddie Yeghiayan. See also the
bibliography in Lewis Edwin Hahn and Paul Arthur Schilpp (eds.),
1986, The Philosophy of W. V. Quine, Peru, IL: Open Court;
second, expanded edition, 1998 (which is complete up to 1997).

1957, “The Scope and Language of Science”, British
Journal for the Philosophy of Science, 8: 1–17; reprinted in
Quine, 1966. (Note: there is an earlier publication with what Quine
describes as “a corrupt text” in ed. Leary, The Unity
of Knowledge, New York: Doubleday, 1955.)